This invention deals with new and novel polysilazane polymers, a method for their preparation, their use to prepare ceramic materials and the ceramic materials prepared thereby. Said invention resides in the use of certain cyclic silazanes or mixtures of such cyclicsilazanes with halogen-containing monosilanes to give the unique polysilazane polymers.
Since about 1975, there has been a renewed effort in the synthesis of preceramic polymers owing to the fact that such polymers have handling properties which allow the formation of shapes and forms prior to ceramification. Thus, several different methods have been developed and disclosed for the preparation of polysilazane polymers that can be converted to silicon nitrogen-containing ceramics and other related materials.
The first reported method was that of Verbeek in U.S. Pat. No. 3,853,567, issued on Dec. 10, 1974 in which methyltrichlorosilane was reacted with methylamine to form methyltris(methylamino)silane. This product could be heated to form a polymer at 520.degree. C. The polymers could then be cured by moist air oxidation at 110.degree. C. and then pyrolyzed to afford a low yielding Si-C-N-O ceramic. Similar materials and techniques were disclosed by Verbeek et. al. in U.S. Pat. No. 3,892,583, issued July 1, 1975.
Some time later, Gaul, in U.S. Pat. No. 4,312,970, issued Jan. 26, 1982, disclosed the preparation of polysilazane polymers that were synthesized by reacting various alkyltrichlorosilanes with a disilazane, such as, {(CH.sub.3).sub.3 Si}.sub.2 NH. In this synthesis, (CH.sub.3).sub.3 SiCl was eliminated as a by-product. These materials could be pyrolyzed at high temperatures to form Si-C-N containing ceramics.
In addition, Gaul, in U.S. Pat. No. 4,404,153 issued July 20, 1982, obtained ceramics materials by pyrolysis of preceramic silazane polymers, which polymers were prepared by reacting chlorine-containing disilanes and disilazanes. These polymers were pyrolyzable to Si-C-N ceramics and prior to pyrolysis, the polymers were capable of being molded, i.e., one could form such shapes as fibers from such polymers.
In another approach, Cannady in U.S. Pat. No. 4,543,344, issued Sept. 24, 1985, prepared polymers by reacting HSiCl.sub.3 and disilazanes. These materials were capable of being pyrolyzed to Si-C-N alloyed ceramics.
Cannady, later, in U.S. Pat. No. 4,540,803, issued Sept. 10, 1985, described a modification to Gaul's process to include the preparation of a polyhydridomethylsilazane polymer from trichlorosilane and hexamethyldisilazane.
Additional polymers have been developed and disclosed by Gaul in U.S. Pat. No. 4,395,460, issued July 26, 1983; U.S. Pat. No. 4,404,153, issued Sept. 13, 1983; Haluska in U.S. Pat. No. 4,482,689, issued Nov. 13, 1984; Seyferth, et al. in U.S. Pat. No. 4,397,828, issued Aug. 9, 1983; and 4,482,669 issued Nov. 13, 1984; Cannady in U.S. Pat. No. 4,535,007, issued Aug. 13, 1985; Bujalski in U.S. patent application Ser. No. 653,003, filed Sept. 21, 1984, now abandoned; Baney, et al. in U.S. patent application Ser. Nos. 652,938, filed Sept. 21, 1984, now abandoned and 652,939, filed Sept. 21, 1984, now abandoned.
What has been discovered are new and novel preceramic polymers, methods for their preparation, their use to prepare ceramic materials and the ceramic materials prepared using such preceramic polymers.